Sukriti Nag

Vascular endothelial growth factor in Alzheimer's disease and experimental cerebral ischemia

Several growth factors have been implicated in the pathogenesis of Alzheimers disease (AD). We considered whether the vascular endothelial growth factor (VEGF) is involved in the vascular pathology associated with most cases of AD. We observed enhanced VEGF immunoreactivity in clusters of reactive astrocytes in the neocortex of subjects with AD compared to elderly controls. VEGF reactivity was also noted in walls of many large intraparenchymal vessels and diffuse perivascular deposits. In addition, we established that astrocytic and perivascular VEGF reactivity was enhanced in cerebral cortex of rats subjected to cerebral ischemia and to chronic hypoxia; experimental conditions known to be associated with astrogliosis and angiogenesis. We suggest the increased VEGF reactivity, also observed in infarcted human brain tissue, implicates compensatory mechanisms to counter insufficient vascularity or reduced perfusion (oligemia) apparent in AD.

Pathology and new players in the pathogenesis of brain edema

Brain edema continues to be a major cause of mortality after diverse types of brain pathologies such as major cerebral infarcts, hemorrhages, trauma, infections and tumors. The classification of edema into vasogenic, cytotoxic, hydrocephalic and osmotic has stood the test of time although it is recognized that in most clinical situations there is a combination of different types of edema during the course of the disease. Basic information about the types of edema is provided for better understanding of the expression pattern of some of the newer molecules implicated in the pathogenesis of brain edema. These molecules include the aquaporins, matrix metalloproteinases and growth factors such as vascular endothelial growth factors A and B and the angiopoietins. The potential of these agents in the treatment of edema is discussed. Since many molecules are involved in the pathogenesis of brain edema, effective treatment cannot be achieved by a single agent but will require the administration of a “magic bullet” containing a variety of agents released at different times during the course of edema in order to be successful.

Role of vascular endothelial growth factor in blood-brain barrier breakdown and angiogenesis in brain trauma

The role of vascular endothelial growth factor (VEGF) in blood-brain barrier (BBB) breakdown and angiogenesis, observed previously in the cerebral cortical cold-injury model, was investigated. Immunohistochemistry was used to assess BBB permeability to plasma fibronectin and to localize VEGF protein in the cortical cold-injury model over a period of 10 min to 14 days post-injury. BBB breakdown to fibronectin in lesion vessels was observed at 10 min post-injury, was maximal between 2 and 4 days and declined gradually thereafter, while occasional perilesional vessels remained permeable up to 6 days. Increased VEGF immunoreactivity occurred later— it was observed in pial vessels after 6 hours (h), and persisted up to day 14. Arterioles within the cold lesion showed VEGF immunoreactivity at 36 h, thus preceding the onset of endothelial proliferation and angiogenesis that occurred from day 3 to day 5. VEGF immunoreactivity was also observed in inflammatory cells and astrocytes. These results indicate that the immediate breakdown of the BBB in the cold lesion is unrelated to VEGF. The presence of mural VEGF in permeable pial vessels and lesional arterioles suggests that VEGF is one of several factors that mediates BBB breakdown in this model. The association of maximal VEGF immunoreactivity with endothelial proliferation and neovascularization suggests that VEGF promotes angiogenesis and repair following brain trauma.

Review: Molecular pathogenesis of blood–brain barrier breakdown in acute brain injury

S. Nag, A. Kapadia and D. J. Stewart (2011) Neuropathology and Applied Neurobiology37, 3–23
Molecular pathogenesis of blood–brain barrier breakdown in acute brain injury

Quantitative estimate of pinocytosis in experimental acute hypertension

SummaryCerebral cortical arterioles in focal neocortical areas develop increased permeability to plasma proteins and protein tracers in experimental hypertensive encephalopathy. The mechanism underlying this increased permeability has been the subject of several studies. In our previous studies of angiotensin-induced acute hypertension, pinocytosis appeared to be the pricipal mechanism for the increased blood-brain barrier (BBB) permeability observed. In the present study pinocytotic activity was assessed quantitatively to determine whether enhanced pinocytosis was confined to the permeable arteriolar segments of hypertensive animals. In addition, the effect of horseradish peroxidase (HRP) itself on the pinocytotic activity of normal cerebral cortical arteriolar endothelium was determined.In 12 rats following administration of HRP, hypertension was induced by an infusion of angiotensin. The animals were perfusion-fixed 90s after the onset of the infusion. Control animals received saline only or HRP only. The area of arteriolar endothelium in cross section was determined by a planimeter from overlapping electron micrographs taken at a constant magnification around the circumference of the vessel wall.Results indicate a significant (P<0.001) increase in the number of pinocytotic vesicles in the permeable arteriolar segments of hypertensive animals as compared with nonpermeable arteriolar segments of the same animals and comparable segments of normotensive rats. In addition, eight times as many vesicles appear to be transporting tracer in the permeable arteriolar segments of hypertensive animals as compared to the nonpermeable segments of the same animals and normotensive animals. HRP alone did not affect the pinocytotic index, there being no difference (P>0.05) in the number of vesicles in normotensive animals receiving saline only and those receiving HRP only. Our previous observation that disruption of endothelial cells or their tight junctions did not occur was confirmed.

A Syndrome of Acute Severe Muscle Necrosis in Intensive Care Unit Patients

Four septic patients and one asthmatic patient are described who developed a severe paralytic disorder in an intensive care unit (ICU), associated with a rise in serum creatine kinase and a severe necrotizing myopathy. All cases had received non-depolarizing muscle blocking agents and large intravenous doses of glucocorticoids. Three patients developed myoglobinuria. No improvement or very little improvement in muscle function was noted in the four fatal cases. The single survivor recovered his strength after 6 months. This syndrome (“necrotizing myopathy of intensive care”) provides one of the differential diagnoses for ICU-acquired weakness. The myopathy appears to have several interdependent causes and it is proposed that these should be classified as myonecrosis “priming” factors (glucocorticoids, myotropic infections, sepsis) and “triggering” factors (non-depolarizing muscle blocking agents).

Nigral pathology and parkinsonian signs in elders without Parkinson disease.

Motor symptoms such as mild parkinsonian signs are common in older persons, but little is known about their underlying neuropathology. We tested the hypothesis that nigral pathology is related to parkinsonism in older persons without Parkinson disease (PD).

Altered Expression of Angiopoietins During Blood-Brain Barrier Breakdown and Angiogenesis

Angiopoietin-1 (Ang-1) and angiopoietin-2 (Ang-2) belong to a novel family of endothelial growth factors that function as ligands for the endothelial-specific receptor tyrosine kinase, Tie-2. Ang-1 reduces endothelial permeability of noncerebral vessels and has a major role in vascular stabilization and maturation, whereas Ang-2 is thought to be an endogenous antagonist of the action of Ang-1 at Tie-2. Expression of these ligands at the mRNA and protein level were studied during both blood-brain barrier (BBB) breakdown and cerebral angiogenesis occurring in the rat cortical cold-injury model by RT-PCR analysis and immunohistochemistry respectively, during a time course of 6 hours to 6 days. In addition, immunohistochemical detection of fibronectin was used to detect BBB breakdown at the lesion site and dual labeling was used to determine whether the vessels demonstrating BBB breakdown expressed endothelial Ang-1 or Ang-2. Endothelial Ang-1 and Tie-2 proteins were present in all cerebral vessels of normal brain including those of the choroid plexuses, whereas both these proteins as well as Ang-2 were present in choroid plexus epithelium and in ependymal cells, suggesting that angiopoietins have an autocrine effect on these cell types as well. In contrast, in the early phase after injury during the known period of BBB breakdown, increased Ang-2 mRNA and protein and decreased endothelial Ang-1 and Tie-2 proteins were observed. Two to 6 days after injury, the progressive increase in Ang-1 mRNA and protein and the decrease in Ang-2 coincided with cerebrovascular angiogenesis. Confocal microscopy showed colocalization of both Ang-1 and Ang-2 in endothelium of lesion vessels, and our observation of colocalization of Ang-1 and Ang-2 in polymorphonuclear leukocytes and macrophages has not been reported previously. This study demonstrates that Ang-1 is an important factor in maintaining normal homeostasis in the brain. Thus Ang-1 therapy may have therapeutic potential in reducing BBB breakdown and the ensuing edema after massive brain injury.

Cerebral changes in chronic hypertension: Combined permeability and immunohistochemical studies

SummaryFocal areas of recent and old necrosis are a consistent finding in brain in chronic hypertension. The possibility that areas represent foci of increased vascular permeability leading to chronic edema and tissue breakdown was investigated in the present study.Rats with chronic renal hypertension demonstrated increased cerebrovascular permeability in focal cortical areas throughout the 7-week period of study. Combined use of tracers and immunohistochemistry demonstrated that these areas of increased permeability with protein extravasation were of different ages. Stage I lesions showed protein in and around arteriolar walls with no cellular reaction indicating that these were very early lesions and corresponded to the findings using HRP as a tracer. Necrosis of the neuropil and an astrocytic and microglial response associated with diffuse collections of protein in the neuropil characterized stage II lesions. Stage III lesions consisted of glial scars or cystic spaces lined by astroglia and associated with absent or sparse protein deposits. Animals that died or were sick prior to killing and had diffuse cerebral edema showed large stage II cortical lesions associated with widespread serum protein extravasation into the white matter of both hemispheres.The principal mechanism resulting in the permeability alterations was enhanced pinocytotic transport of tracer across the endothelium of penetrating cortical arterioles. Vascular occlusion by thrombi was not observed in pial or intracerebral vessels.Our findings are consistent with the hypothesis that increased vascular permeability leads to chronic edema and tissue necrosis in chronic hypertension.

The blood–brain barrier and cerebral angiogenesis: lessons from the cold-injury model

Brain injury is associated with an initial blood-brain barrier (BBB) breakdown, which can be life threatening. A second phase of BBB breakdown accompanies the angiogenesis occurring at the lesion margins. Studies of the molecular mechanisms involved in these processes are essential to determine targets for therapeutic intervention, as well as the time periods during which therapeutic intervention could ameliorate brain damage and thus improve the clinical outcome.